1) Field of the Invention
This invention relates an impeller pump useful as an electric-motor-operated fuel pump for an automotive vehicle to pump liquid fuel from a fuel tank through a fuel handling system to an engine that powers the vehicle. More particularly, the invention relates to improvements in vapor venting efficiency that improve pump efficiency.
2) Background Information
In an automotive vehicle that is powered by an internal combustion engine, fuel may be pumped through a fuel handling system of the engine by an in-tank, electric-motor-operated fuel pump. Various features for improving the efficiency of such pumps are known in the art. One of those features is a vent hole for venting liquid entrained vapor from the pumping chamber of the pump.
Examples of various vapor venting systems in pumps are shown in various patents, including U.S. Pat. Nos. 4,591,311; 5,284,417; 5,330,319; 5,580,213; 5,662,455; and JA 0175297.
U.S. Pat. No. 4,591,311 shows an impeller pump whose pumping chamber comprises a channel having a length that runs circumferentially about the main axis of the pump. An inlet to the channel and an outlet from the channel are in excess of 270.degree. apart about the pump axis. A vapor vent hole extends out of the pumping chamber through a side wall of the pump casing parallel to the pump axis. The vent hole is spaced angularly from the inlet at an end of an upstream portion of the channel that has a larger cross sectional area than a following downstream portion of the channel that leads to the outlet. The vent hole intersects the channel just ahead of a step in the radially inner wall of the channel that demarcates the larger upstream portion from the smaller downstream portion.
U.S. Pat. No. 5,284,417 shows a pumping chamber channel having a vapor vent hole extending through a side wall of the pump casing parallel to the pump axis. The vent hole is spaced angularly from an inlet at an end of an upstream portion of the channel. As the upstream portion of the channel approaches the vent hole, the portion of its cross section that is enlarged relative the cross section of its downstream portion progressively contracts in the radial direction, providing a tapering transition to the vent hole.